Simultaneous capture of motion information in a video can provide valuable information in many applications such as, for example, biometrics where a detectable brainwave signal or some repetitive physical motion such as eye blinks, twitches, ticks, and the like, is desired to be extracted from the video. Another application is video-based traffic enforcement where a signal relating to tire rotational speed is desired to be measured. In healthcare, the ability to monitor patient physiological function by non-contact means is highly desirable in monitoring, for example, neonatal patients, burn or trauma patients, sleep studies, and other cases where a continuous measurement of a patient physiological signal is required without the use of adhesive patches, clips, straps, and the like, which may be impractical or lead to patient discomfort, dependency, loss of dignity, and further may fail due to wires coming lose or moving. The teachings hereof are directed to extracting a periodic signal from a video of a scene.